The present invention relates to a brewing bag made of a liquid-permeable filter material for use in a filter coffee brewing apparatus. This invention also relates to a filter coffee brewing apparatus provided with such a brewing bag. Furthermore, this invention relates to a process for the production of a brewing bag for a filter coffee brewing apparatus.
Commercial filter coffee brewing apparatuses, such as those used in particular in aeroplane kitchens, normally use ground coffee which is packed into brewing bags. Such filter coffee brewing apparatuses typically comprise a feed head for the provision of hot brewing water under overpressure, a usually cylindrical brewing inset for holding a brewing bag containing the coffee, a lifting device for bringing the brewing inset into leakproof arrangement with the feed head, and a collecting vessel for the brewed coffee.
The brewing bags normally used for these purposes which, depending on their size, contain up to about 200 g of coffee take the shape of a round pad of approximately lenticular cross section. This bag consists essentially of two circular pieces consisting of a liquid-permeable filter material which pieces are joined along their circumferential edges via cold- or hot-pressing/-stamping. The joined circumferential edges form a radial circumferential flange in the centre plane of the bag.
For their use these pad-shaped bags, which match the size of the brewing inset, are inserted into the cylindrical brewing inset and neatly stuffed in by hand in such a way that the circumferential flange formed by the circumferential edges folds upwards and snuggles as smoothly as possible to the interior wall of the brewing inset. Experience shows that due to the shape of the flange and its own small yet present stiffness the flange in most cases does not snuggle closely and evenly to the interior wall but is usually slightly wavy. However, this waviness creates unwanted secondary flow paths for the brewing water to flow past the brewing bag, which is additionally promoted by the overpressure of the brewing water. However, the fact that part of the brewing water flows via the secondary flow paths past the coffee in the brewing bag substantially impairs the quality of the coffee brewed in this manner. However, as modem tourists have increased demands regarding taste and as the airline companies constantly seek to improve their services also in the culinary area, very high demands are made on the quality of the brewed coffee which the conventional filter coffee brewing apparatuses cannot always and reproducibly fulfil.
From the generic EP-A-0 249 700 a filter coffee brewing apparatus with a brewing bag consisting of two layers of filter is known which, when in the state of being inserted in the brewing inset, has essentially about the shape of a truncated cone and matches the brewing inset, with a bottom part, a jacket part which forms one piece with the bottom part and a cover part, which cover part together with the jacket part forms a relatively broad or high double-walled protruding collar. The bottom part and the jacket part are formed by the lower filter layer and the cover part by the upper filter layer. The two filter layers are closely connected with each other in the collar area. In the brewing device a hot water outlet is provided above the brewing bag through which hot brewing water is led to the cover part of the bag when in operation. The headroom between the bottom of the brewing inset and the hot water outlet is kept relatively small so that the hot water outlet is at a relatively short distance above the cover part of the (still dry) brewing bag. When hot water is led in, the cover part of the brewing bag inflates due to the heat of the air escaping from the coffee powder within and through this snuggles relatively tightly around the hot water outlet. This is said to result in the brewing water being led centrally into the brewing bag and as a consequence the coffee powder is said to be well extracted.
Starting from the generic brewing bag, it is the object of this invention to create another brewing bag which on the one hand requires no complicated manipulation when inserting the brewing bag into the brewing inset and on the other hand warrants an optimal brewing result while preventing quality impairing secondary flow paths for the brewing water.
The object of this invention is achieved by forming the brewing bag of this invention in a special way.
The inventive shape of the brewing bag does not only warrant an optimal brewing process but also simplifies the handling since the bag can be effortlessly inserted into the brewing inset without needing to be stuffed in. This is also an advantage from the point of view of hygiene.
Many individual factors must be carefully coordinated for the high demands on the quality and taste of coffee to be met. These encompass also in particular the types of coffee used and their provenance, their mixture, degree of roasting, degree of grinding and so forth. The inventive brewing bag prevents that the quality standards that the coffee producer achieved at great expenditure are partly or even entirely lost in the brewing process.